Shrouded impeller



Jan. 13, 1953 v, MOORE 2,625,365

SHROUDED IMPELLER Filed Feb. 26, 1949 2 SHEETS-SHEET l INVENTOR VINCENTMEIURE ATTORNEY Jan. 13, 1953 v. MOORE 2,625,365

SHROUDED IMPELiLER Filed Feb. 26, 1949 2 SHEETS-$HEET 2 I INVENTORVINCENT MDDRE ATTORNEY Patented Jan. 13, 1953 SHROUDED IMPELLER VincentMoore, Ridgewood, N. J., assignor to Curtiss-Wright Corporation, a.corporation of Delaware Application February 26, 1949, Serial No. 78,611

1 Claim.

This invention relates to bladed rotors for turbines, compressors,blowers or the like and is more particularly directed to such rotorshaving blades extending therefrom and having a shroud secured to andextending between or across the outer or tip ends of said blades.

Bladed rotors for turbines, compressors, blowers or the like have beenprovided with a shroud formed integral with the outer or tip ends of therotor blades, for example by machining the rotor, with its blades andshroud, from one piece of metal. Such one piece constructions areobviously quite difficult to fabricate and expensive. An object of thisinvention comprises the provision of a novel shrouded rotor constructionin which the shroud, after having been separately fabricated, is securedto the outer or tip ends of the rotor blades. In accordance with thepresent invention, separately formed shroud elements are disposedbetween the tip ends of the rotor blades, said shroud elements beingwelded or brazed to said blades in a manner to allow for shrinkage ofthe shroud following the welding or brazing operation without imposingundesirable stresses in said welded or brazed junctions.

Other objects of the invention will become apparent upon reading theannexed detailed description in connection With the drawing in which:

Figure 1 is an end view of a centrifugal compressor rotor embodying theinvention;

Figure 2 is a sectional View taken along line 2--2 of Figure 1;

Figure 3 is a view taken along line 3-3 of Figure 1;

Figure 4 is a perspective view illustrating a, portion of thecentrifugal compressor rotor of Figures 1-3;

Figure 5 is a sectional view, similar to Figure 2, but of an inducer orentrance section for the centrifugal compressor of Figures 1-4;

Figure 6 is an end view taken along line 6-45 of Figure 5;

Figure '7 is an enlarged view of a portion of Figure 3; and

Figures 8, 9, l0, and 11, are views similar to Figure 7 but of modifiedconstructions.

Referring first to Figures 1 to 4, the invention is illustrated inconnection with the bladed rotor of a centrifugal compressor [0. As willbecome apparent however, the invention is not limited to this type ofbladed rotor. For example, the invention is equally applicable to axialflow compressors, to axial or centrifugal blowers and to turbines of theaxial or radial flow types.

The compressor I0 is provided with a plurality ofcircumferentially'spaced fiat blades l2 extending radially from its hub14, said hub being provided with internal splines Hi to which a drivingshaft is adapted to be drivably connected. A plurality of shroudelements I8 are provided, each of said shroud elements being disposedbetween the outer or tip ends of a pair of adjacent blades I2. Theconstruction of said shroud elements I8 is best seen in Figure 4.

Each shroud element l8 comprises adeck 20 having a pair of flanges 22disposed along opposite edges of said deck 20, so that each shroudelement l8 ha a channel-shaped cross-section. Each shroud element isshaped so that its deck 20 bridges the gap between the outer or tip endsof a pair of adjacent blades l2 between which said shroud element isdisposed. In addition the flanges 22, of each shroud element 18, engagethe sides of the outer or tip ends of its associated blades l2 andextend inwardly toward the root ends of said blades. The flanges 22 aresecured to their engaged blades l2 by a, metallic fused junction, forexample by welding or brazing, as hereinafter described. With a shroudelement I8 secured in position between each pair of adjacent rotorblades l2, the tip ends of the rotor blades are provided with a shroudconstruction rigid with said blades.

Centrifugal compressors are commonly provided with an inducer or axialentrance section, for example as disclosed in Patent Number 2,399,852issued to Campbell et a1. Figure 5 and 6 illustrate the application ofthe present invention to such an inducer section.

In Figures 5 and 6, there is illustrated an inducer or axial entrancesection 30 for th centrifugal compressor Ill. The inducer section 30comprises a hub 32 which is adapted to be coaxially secured to the hub Mof the centrifugal compressor 10. In addition said inducer section 30has a plurality of circumferentially spaced blades 34 extendingsubstantially radially therefrom. The inducer blades 34 are designed tocomprise continuations of the blades l2. Thus, the downstream ends ofthe blades 34 are adapted to abut against the upstream ends of thecentrifugal compressor blades I2 and the upstream ends of the inducerblades 34 are curved into the direction of rotation of the compressor.The shape of the inducer blades 34 and their relation to the flatcentrifugal compressor blades l 2 is conventional and is more fullydescribed in the aforementioned patent of Campbell et al.

A shroud element 36 is secured between the outer or tip ends of eachpair of adjacent inducer blades 34 in a manner similar to the mode ofsecurement of the shroud element I8 to their blades l2. Thus, eachshroud element 36 has a pair of flanges 38 extending from opposite edgesof its deck 40 toward the roots of its pair of adjacent inducer blades34. In addition said pair of flanges 38 are disposed against and securedto the outer or tip ends of the :pair of adjacent blades 34. With theshroud elements 36 secured in position between the inducer blades 34,said inducer blades are provided with a shroud construction rigid withthe outer or tip ends of said blades and forming a continuation of theshroud OD- t tion provided by the shroud elements L8, 7

The shape of each said shroud element must obviously conform to theinter-blade space in which said shroud element is disposed. Accordinglyexcept for their shape, the shroud elements [8 and 3B are similar. Theshroud elements [8 are secured to the rotor blades .12 .of the mainportion of a centrifugal compressor in which the fluid flow is primarilyradial relative .to the rotor axis while the shroud elements .35 aresecured to the rotor blades .34 .of said centrifugal compressor inducersection in which the flow is primarily axial relative to the rotor axis.Accordingly, it should be apparent that the rotor of any ,compressor,blower, turbine or the like, having a plurality of blades extendingtherefrom, can, in ac cordance with the present invention, be providedwith a shroud construction rigid with the outer or tip-ends of the rotorblades.

The specific manner in which the shroud elements are secured to therotor blades is best illustrated in Figures 7 to 10. Reference is firstmade to Figure 7. wh c comp i e a nl r ement of that portion of Figure 3enclosed by the circular line 39. In Figure '7 the shroud element 18 isbrazed to its pair of adjacent blades 12 as indicated by the brazedjunction 40. Inaddition, the corner between each shroud flange 22 andits deck 20 is curved as indicated at 42 whereby the deck end of eachflange 22 bends or diverges away from the tip of its adjacent blade ,I2to provide an outwardly facing diverging groove 44 therebetween. Themagnitude of this divergence is such that the brazed junction 43 betweeneach blade l2 and its shroud flange 22 is disposed inwardly of the innersurface of its shroud deck 20. With this construction, any shrinkage ofa shroud .deck 20, as it cools after the brazing operation, is taken upy bending between said deck 20 and its flanges 22. In this way, thebrazed junction 40 between each shroud flange 22 and its blade 12, isnot subjected to appreciable tensile stresses as a result of shrinkageof its deck 29 after the brazing operation. Obviously, if the brazedjunction 48 were to extend to the outer surface of its deck 20, then anyshrinkage of said deck would subject said brazed junction to hightensile stress. However, with the brazed junction M! disposed inwardlyof the inner surface of its deck 26, shrinkage of said deck merelyresults in bending between said deck and its flanges 22 so as toincrease the corner angle therebetween.

It has been found that, if the radius of curvature at the inside of thecorner #2, between each flange 22 with its deck 2'8, is at least equalto the thickness of the shroud material, the groove 44 is sufiicientlywide so that the subsequently formed brazed junction 4!? will bedisposed sufficiently inwardly of the inner surface of its deck 2.9 toavoid the creation of any appreciable tensile s r s s i tunction as a rsult of shrinkage of said deck after the brazing operation.

Figure 8 illustrates a modification of Figure 7. In Figure 8, a shroudelement 50 comprises a deck 52 having a pair of inturned flanges 54adapted to be secured against the sides of their respective adjacentblades I2 by brazing at 56. In Figure 8, the deck end of each flange 54is reduced in thickness to provide a groove 58 between it'he .outer ortip end of the adjacent blade .12 and the deck .end of said flange. Thegrooves 58 are provided to prevent the formation of a brazed junctionbetween a blade l2 and the adjacent reduced thickness portion of aflange 54.

The shroud elements l8 and 50 of Figures 7 and .8, respect ively,areotherwise similar.

The depth of each groove 58 is greater than the thickness of theadjacent deck 52 so that the brazed junction 58, securing each flange 54to a blade l2, is disposed inwardly of the inner suriac of said deck.Thus the function of the grooves 58, in Figure 8, is the same as thefunction ,of the grooves 44, in Figure 7 Accordingly, shrinkage .of adeck .52 of a shroud element after the brazing operation, securing saidshroud element .50 to the blades 12, is compensated for by bendingbetween said deck .52 and its flange 5:, without imposing large tensilestresses on its brazed junctions 56. As ,a precautionary measure .or ifnecessary, astainless steel plate fill may be temporarily inserted in.each groove 58, during the brazing operation, to prevent the :formationof a "brazedjunction across the groove 56.

Figure 9 illustrates a still further modification of Figure 7. In Figure9,, ,a shroud element 10 comprises a deck 72 and side flanges 14 spotwelded to the blades 12 as indicated ,at 15. In spot Welding, theposition of each spot weld junc- .tion 116 can be accurately controlledwithout regard to the shape of the space between each flange 7d and itsassociated blade l2. Accord ingly the shroud elements 70 need not .beformed to provide a groove between its side flangeslll and its adjacentblades 12 as in the case of the grooves 44 and 58 of Figures 7 and v8respectively. In "Figure ,9, the spot weld junctions 76 are locatedinwardly of the adjacent inner surface of its associated deck '72. Withthis arrangement, any shrinkage of said deck after the spot weld ngoperation, merely causes bending between its flanges l4 and said deckwithout imposing large tensile stresses on the spot weld junctions.-

Figure 10 illustrates a structure similar to F ure 7 but the centrifugalcompressor .blades l2 of Figure 10 diiTer from the blades 12 of .Ftigure7 in that the blades 12' do not project beyond their brazed junctions4-0 with the shroud elements [8. That is, the portion .of each vane l2.of Figure? projecting beyond its brazed junction on, has been removedin Figure 10. The structure of Figures 7 and 10 are otherwise similar.With this ancture of Figure 10, a relatively large external groove isformed between each pair of shroud elements 12, thereby increasing thepumping losses caused by irregularities in the ,outer surface of theshroud construction above the corresponding losses with the shroudconstruction ,of Figure 7. If said pumpin losses are negligible or notobjectionable then the structure of Figure ,10 may be preferred becauseit has the following advantage, namely that the outer edge of each yane12' provides a positive outer limit for its brazed junction to.Accordingly, if the inner surface-of each shrouddeck 2D is disposedoutwardiy-cf t outer edg o ts assoc ted vanes I1 its raz d auncticn to,canpo r ssiblyext nd 011twardilybeyondsaidinner surface re ardless ,ofthe curvature of the corners 42 between said deck 20 and each of itsflanges 22. Obviously the structure of Figure 8 may be modified in asimilar manner by shortenin the compressor blades l2 so as not to extendbeyond their brazed junctions with their shroud elements.

Figure 11 illustrates still another modification of the shroud elements.In Figure 11, shroud elements 80 and 80' each comprise a deck 82 havingside flanges 84 depending therefrom. Reference numeral 80 indicates theshape of a shroud element prior to welding or brazing said element tothe rotor blades 12 and reference numeral 80' indicates the shape ofsaid shroud element after welding or brazing said element to saidblades. As indicated at 86, each shroud element is welded \ur brazed) tothe adjacent blades l2 at the outer or tip ends of said blades and atthe junction or its flanges 84 with its deck 82. Accordingly each weldedor brazed junction 86 is disposed substantially in the plane of itsassociated deck 82 so that shrinkage of said deck, after said spotwelding operation, cannot be compensated for by bending of its flanges85 relative to said deck 82. As illustrated, however, each deck 82, asfabricated, is bowed slightly outwardly so that when said deck shrinks,after the welding operation, the deck merely straightens out asindicated at 89 thereby avoiding the creation of large tensile stressesin the welded or brazed junction 86. Obviously, this same result may beobtained by bowing the decks 82 inwardly instead of outwardly.

In each of the species of Figures '7 to 11 inclusive, the shroudelements and their brazed or welded junctions to the rotor blades aresuch that the shrinkage of said elements following the brazing orwelding operation does not impose large stresses on the welded junction.It is possible to weld or braze each shroud element separately and tocompensate for shrinkage of said shroud elements by deflection of therotor blades. Thus, the deck of each shroud element could be madeslightly larger than the gap between the tip ends of a pair of rotorblades. Then, prior to the securement of a shroud element between a pairof rotor blades, at least one of said rotor blades could be deflectedslightly to widen the gap between said pair of blades such that thesubsequent shrinkage of said shroud element merely undoes saiddeflection. Obviously, however, shrinkage at the last shroud element tobe secured in place on a particular rotor could not be compensated forin this manner, but could be compensated for by one of the constructionsillustrated in Figures '7 to 11 inclusive.

In all of the various species the tip end of the impeller blades I2 orl2 could obviously be notched to receive the side flanges of the shroudelements so that each said flange forms a smooth continuation of theadjacent surface of its associated impeller blades.

While I have described my invention in detail in its present preferredembodiment, it will be obvious to those skilled in the art, afterunderstanding my invention, that various changes and modifications maybe made therein without departing from the spirit or scope thereof. Iaim in the appended claim to cover all such modifications.

I claim as my invention:

In a turbine, compressor, blower or the like having an annular fluidflow path; a rotor membar; a plurality of pircumferentially-spacedblades having a one-piece construction with said rotor member andextending therefrom into said fluid flow path; a plurality of shroudelements each disposed between a pair of adjacent blades, each of saidshroud elements having a deck portion bridging the gap between the tipends of its pair of blades from substantially the upstream to thedownstream ends of said blades and having a pair of flanges extendinginwardly only part way toward the root ends of said blades from oppositeedges of said deck portion; and a brazed junction between each saidflange and the adjacent blade and extending to the tip end of saidblade, each shroud element deck portion bein disposed outwardly beyondthe tip end of each adjacent blade.

VINCENT MOORE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,292,830 McCain Jan. 28,19192,390,504 Berger Dec. 11, 1945 FOREIGN PATENTS Number Country Date563,458 Germany Nov. 5, 1932

